Standard practice in the operation of a compression-ignition engine is to introduce the liquid fuel into the combustion chamber at high pressures near the end of the compression stroke of the piston. This promotes rapid mixing and evaporation of the fuel and leads to autoignition and combustion with the air previously inducted into the chamber. Autoignition refers to the condition wherein the fuel spontaneously ignites under the temperature and pressure conditions existing within the chamber.
Fuels which readily ignite under the conditions within the chamber require only a single nozzle for injection of the fuel into the chamber, as in most standard diesel combustion engines.
Some fuels, however, such as methanol and ethanol do not readily autoignite. Such fuels possess desirable properties such as low exhaust emissions which make them desirable fuels for combustion engines. Thus, efforts have been made to promote ignition of these fuels.
It is known that ignition can be promoted with an injection of a small amount of a readily ignitable fuel such as diesel fuel. Typically, these so called "pilot fuels" are injected into the combustion chamber in advance of the primary fuel injection. Under the conditions of the combustion chamber, the pilot fuel ignites which causes ignition and combustion of the primary fuel.
It is also known to inject a single fuel of uniform composition but poor ignition quality into an engine using double injection for each combustion event. Such staged or "staggered" injection systems also employ an injection of pilot fuel in advance of the main injection, allowing the injected pilot fuel to undergo physical and chemical conditioning and to ignite. This aids the ignition and combustion of the main fuel charge having the identical chemical composition. This system is particularly suited for fuels having poor ignition quality.
In order to introduce both the primary and pilot fuels to the combustion chamber, it is known to use two separate and independent fuel injection systems. Each system is provided with its own means of pressurizing the fuel and injecting the fuel into the combustion chamber as an atomized spray. Specifically, one of the fuel injection systems will have a nozzle particularly suited for injecting the primary fuel and the other the pilot fuel.
One of the disadvantages of a two nozzle system is that under typical operating conditions it is preferred to introduce the fuel at or near the physical center of the combustion chamber. The center of the combustion chamber is usually occupied by the primary fuel nozzle so that the pilot fuel nozzle must be placed in a less desirable location at the periphery of the chamber.
It is desirable to be able to convert an engine from one which is powered by an autoignitable fuel such as diesel fuel to one which can use a non-autoignitable fuel such as methanol and ethanol in order to avoid the cost of producing two different types of engines.
However, such conversion is rendered difficult and costly when a one nozzle system is converted to a two nozzle system since it is often necessary to modify major parts of the engine including the cylinder head.
It would therefore be desirable to provide a fuel injection system which can meter two different fuels to the combustion chamber through the same nozzle, and which can readily be removed and replaced by a system for injecting only a single fuel to the chamber.
It is therefore an object of the present invention to provide a fuel injection system for injecting both a primary and pilot fuel from a single nozzle into a combustion chamber.
It is another object of the invention to provide a fuel injection system which may be readily installed and removed from an engine.
It is a further object of the invention to employ a novel valve within the nozzle which enables one of the fuels to be transported through the valve.